What does the symbol 0 mean in a string-literal

Question

Consider following code   char str      Hello 0     What is the length of str array  and with how much 0s it is ending

User · Accepted Answer

sizeof str is 7 - five bytes for the  Hello  text  plus the explicit NUL terminator  plus the implicit NUL terminator   strlen str  is 5 - the five  Hello  bytes only   The key here is that the implicit nul terminator is always added - even if the string literal just happens to end with  0  Of course  strlen just stops at the first  0 - it can t tell the difference   There is one exception to the implicit NUL terminator rule - if you explicitly specify the array size  the string will be truncated to fit   char str 6     Hello 0      strlen str    5  sizeof str    6  with one NUL  char str 7     Hello 0      strlen str    5  sizeof str    7  with two NULs  char str 8     Hello 0      strlen str    5  sizeof str    8  with three NULs per C99 6 7 8 21    This is  however  rarely useful  and prone to miscalculating the string length and ending up with an unterminated string  It is also forbidden in C

User · Answer

The length of the array is 7  the NUL character  0 still counts as a character and the string is still terminated with an implicit  0  See this link to see a working example  Note that had you declared str as char str 6    Hello 0   the length would be 6 because the implicit NUL is only added if it can fit  which it can t in this example        sect  6 7 8 p14 An array of   character type may be initialized by a   character string literal  optionally   enclosed in braces  Sucessive   characters of the character string   literal  including the terminating   null character if there is room or if   the array is of unknown size    initialize the elements of the array    Examples  char str      Hello 0      sizeof    7  Explicit   Implicit NUL    char str 5    Hello 0      sizeof    5  str is  Hello  with no NUL  no longer a C-string  just an array of char   This may trigger compiler warning    char str 6    Hello 0      sizeof    6  Explicit NUL only    char str 7    Hello 0      sizeof    7  Explicit   Implicit NUL    char str 8    Hello 0      sizeof    8  Explicit   two Implicit NUL

User · Answer

char str     Hello 0     That would be 7 bytes   In memory it d be   48 65 6C 6C 6F 00 00 H  e  l  l  o   0  0   Edit      What does the  0 symbol mean in a C string  It s the  end  of a string  A null character  In memory  it s actually a Zero  Usually functions that handle char arrays look for this character  as this is the end of the message  I ll put an example at the end  What is the length of str array   Answered before the edit part  7 and with how much 0s it is ending  You array has two  spaces  with zero  str 5  str 6    0  0   Extra example  Let s assume you have a function that prints the content of that text array  You could define it as   char str 40     Now  you could change the content of that array  I won t get into details on how to   so that it contains the message   This is just a printing test  In memory  you should have something like   54 68 69 73 20 69 73 20 6a 75 73 74 20 61 20 70 72 69 6e 74 69 6e 67 20 74 65 73 74 00 00 00 00 00 00 00 00 00 00 00 00   So you print that char array  And then you want a new message  Let s say just  Hello   48 65 6c 6c 6f 00 73 20 6a 75 73 74 20 61 20 70 72 69 6e 74 69 6e 67 20 74 65 73 74 00 00 00 00 00 00 00 00 00 00 00 00   Notice the 00 on str 5   That s how the print function will know how much it actually needs to send  despite the actual longitude of the vector and the whole content

User · Answer

What is the length of str array  and with how much 0s it is ending    Let s find out   int main       char str      Hello 0     int length   sizeof str   sizeof str 0         sizeof array  is the bytes for the whole array  must use a real array  not      a pointer   divide by  sizeof array 0    sometimes sizeof  array is used       to get the number of items in the array   printf  array length   d n   length     printf  last 3 bytes   02x  02x  02x n            str length - 3   str length - 2   str length - 1      return 0

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Banging my usual drum solo of JUST TRY IT  here s how you can answer questions like that in the future     cat junk c  include  lt stdio h gt   char  string    Hello 0    int main int argv  char   argc        printf  -- gt  s lt -- n   string       gcc -S junk c   cat junk s       eliding the unnecessary parts       LC0       string  Hello       string            LC1       string  -- gt  s lt -- n         Note here how the string I used for printf is just  -- gt  s lt --- n  while the global string is in two parts   Hello  and      The GNU assembler also terminates strings with an implicit NUL character  so the fact that the first string   LC0  is in those two parts indicates that there are two NULs   The string is thus 7 bytes long   Generally if you really want to know what your compiler is doing with a certain hunk of code  isolate it in a dummy example like this and see what it s doing using -S  for GNU -- MSVC has a flag too for assembler output but I don t know it off-hand    You ll learn a lot about how your code works  or fails to work as the case may be  and you ll get an answer quickly that is 100  guaranteed to match the tools and environment you re working in

User · Answer

Specifically  I want to mention one situation  by which you may confuse   What is the difference between   0  and      The answer is that   0  represents in array is  0 0  and    is  0    Because   0  is still a string literal and it will also add   0  at the end of it  And    is empty but also add   0    Understanding of this will help you understand   0  deeply

[c++] What does the symbol \0 mean in a string-literal?

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